1. Field of the Invention
The present invention relates to a battery status detecting method and a battery status detecting apparatus for detecting the status of a secondary battery.
2. Description of the Related Art
Open circuit voltage characteristics of a secondary battery indicating a relationship between the charge rate and the open circuit voltage of a secondary battery is conventionally assumed to be substantially constant regardless of degradation or changes in the usage conditions of the secondary battery. For example, Japanese Laid-Open Patent Publication No. 2001-231179 discloses a battery capacity detecting method using such open circuit voltage characteristics. Specifically, the disclosed battery capacity detecting method involves measuring the open circuit voltage during a rest period of a secondary battery and estimating the charge rate of the secondary battery at the time of the measurement based on the measured open circuit voltage and the open circuit voltage characteristics of the secondary battery obtained beforehand. It is noted that the above publication further discloses a method of estimating the full charge capacity of the secondary battery based on the charge rates of the secondary battery before and after performing battery charging operations and the amount of power charged to the secondary battery during the battery charging operations, and a method of estimating the remaining capacity of the secondary battery after completion of the battery charging operations based on the charge rate after performing the battery charging operations and the full charge capacity.
However, there are secondary batteries that have open circuit voltages with temperature characteristics. Accordingly, when the battery status such as the charge rate of a secondary battery is detected based on open circuit voltage characteristics represented by a curve with the vertical axis indicating the open circuit voltage and the horizontal axis indicating the charge rate, detection errors of the charge rate may vary even when detection errors of the open circuit voltage are the same. Specifically, detection errors of the charge rate may be greater in the case where the open circuit voltage characteristics of the secondary battery are represented by a curve having a relatively gentle slope compared to a case where the open circuit voltage characteristics of the secondary battery are represented by a curve having a relatively steep slope. Thus, it is desirable that the temperature characteristics of the open circuit voltage of the secondary battery be taken into consideration in detecting the battery status, such as the charge rate of the secondary battery.